1. Field of the Invention
This invention relates to a process for recovering and recycling waste methanesulfonic acid (MSA) and phosphorous acid (H.sub.3 PO.sub.3) in a bisphosphonation process by separating and dehydrating a mixture of methanesulfonic acid and phosphorous acid by sequential distillation, for reuse in the process.
2. Brief Description of Disclosures in the Art
Alendronate sodium, 4-amino-1-hydroxybutylidene-1-bisphosphonic acid monosodium trihydrate, is a promising new agent for combatting bone resorption in bone diseases including osteoporosis, particularly in post-menopausal women. The compound, utility and method of preparation are described in U.S. Pat. Nos. 4,922,007 and 5,019,651, both assigned to Merck & Co., Inc.
Large scale processes, as described in the above patents, for producing alendronate sodium generate large volumes of materials containing high concentrations of soluble phosphorus-containing materials (PO.sub.X) including sodium salts of phosphates, phosphites, pyrophosphates, and methanesulfonic acid/phosphorous acid.
Generally, wastewater treatment processing (WWTP) facilities can handle on a total daily basis about 1-10 ppm (mg/L) phosphorus per liter and 50-500 ppm (mg/L) of MSA.
However, the alendronate process can generate as much as 500 mg of phosphorus and over 1000 mg MSA per liter of waste per day greatly exceeding the allowable limits in many geographic regions for wastewater processing and discharge of effluent.
General methods for dealing with this problem have included industrial incineration, storage and disposal of wastewater materials over extended periods of time at the allowable environmentally imposed limits for PO.sub.X and MSA.
However, incineration suffers from high cost due to the volume of wastes, the low BTU value of the salt solutions and their potential for acidic emissions which could lead to acid rain. Disposal via wastewater treatment, WWT, suffers from the requirements of large corrosion resistant storage tanks used for extended time periods and expensive labor costs due to increased levels of monitoring of WWTP operating parameters.
Other methods include biodegradation of methanesulfonic acid (MSA) using an activated sludge and oxidizing phosphorous acid (H.sub.3 PO.sub.3) to phosphoric acid (H.sub.3 PO.sub.4) for easier removal.
However these methods suffer the disadvantage of only being able to process small portions of the waste PO.sub.X /MSA for a given biodegradation cycle. Furthermore, efficient biodegradation of MSA can potentially interfere with the ability of the WWTP to degrade other more easily oxidizable substrates. Optimal conditions for the biodegradation of MSA are considerably different from standard WWTP operating conditions, vary from site to site and are disruptive to production scheduling.
What is desired in the art is a process for recovering and recycling methanesulfonic acid, MSA, and phosphorous acid H.sub.3 PO.sub.3, in an environmentally safe, efficient and cost-effective manner, that has minimal impact on typical WWTP operating parameters.